U.S. patent application number 12/598548 was filed with the patent office on 2010-05-06 for exhaust purification apparatus for an engine.
This patent application is currently assigned to MITSUBISHI FUSO TRUCK AND BUS CORPORATION. Invention is credited to Hiroaki Fujita, Satoshi Hiranuma, Shinichi Saito, Yoshinaka Takeda, Satoshi Yamazaki.
Application Number | 20100107612 12/598548 |
Document ID | / |
Family ID | 39943424 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100107612 |
Kind Code |
A1 |
Yamazaki; Satoshi ; et
al. |
May 6, 2010 |
EXHAUST PURIFICATION APPARATUS FOR AN ENGINE
Abstract
An exhaust purification apparatus for an engine has a first
casing (17) that is interposed in an exhaust path (13); a second
casing (23) that is set downstream of the first casing (17) and
contains an exhaust purification device (24); a connecting pipe
(22, 41, 51) that connects the first casing and the second casing
(23) to each other and includes an insertion portion that is
inserted in the first casing (17); and an injection nozzle (27, 52)
that has a tip end inserted in the connecting pipe (22, 41, 51) and
injects an auxiliary agent from the tip end. The insertion portion
of the connecting pipe (22, 41, 51) is provided with a plurality of
through-holes (22a, 41a, 41b, 51a) connecting the inside and the
outside of the connecting pipe (22, 41, 51), so that the exhaust
gas contained in the first casing (17) is introduced into the
connecting pipe (22, 41, 51) through the through-holes and guided
towards the second casing (23).
Inventors: |
Yamazaki; Satoshi;
(Kawasaki-shi, JP) ; Takeda; Yoshinaka;
(Kawasaki-shi, JP) ; Fujita; Hiroaki;
(Kawasaki-shi, JP) ; Hiranuma; Satoshi;
(Kawasaki-shi, JP) ; Saito; Shinichi;
(Kawasaki-shi, JP) |
Correspondence
Address: |
ROSSI, KIMMS & McDOWELL LLP.
20609 Gordon Park Square, Suite 150
Ashburn
VA
20147
US
|
Assignee: |
MITSUBISHI FUSO TRUCK AND BUS
CORPORATION
Kawasaki-shi, Kanagawa
JP
|
Family ID: |
39943424 |
Appl. No.: |
12/598548 |
Filed: |
April 22, 2008 |
PCT Filed: |
April 22, 2008 |
PCT NO: |
PCT/JP2008/057769 |
371 Date: |
November 2, 2009 |
Current U.S.
Class: |
60/295 ; 60/297;
60/303; 60/310 |
Current CPC
Class: |
F01N 3/2882 20130101;
F01N 13/08 20130101; F01N 13/009 20140601; F01N 2470/02 20130101;
B01D 53/9477 20130101; B01D 53/90 20130101; F01N 3/2892 20130101;
F01N 2610/02 20130101; B01D 2251/2067 20130101; F01N 13/0097
20140603; Y02T 10/24 20130101; F01N 3/2066 20130101; Y02T 10/12
20130101; B01D 53/9431 20130101; F01N 3/24 20130101; F01N 3/035
20130101; F01N 3/106 20130101; F01N 3/0253 20130101 |
Class at
Publication: |
60/295 ; 60/310;
60/297; 60/303 |
International
Class: |
F01N 3/023 20060101
F01N003/023; F01N 3/04 20060101 F01N003/04; F01N 3/035 20060101
F01N003/035; F01N 3/10 20060101 F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 1, 2007 |
JP |
2007-120681 |
Claims
1. An exhaust purification apparatus for an engine comprising: a
first casing that is interposed in an exhaust passage of the
engine; a second casing that is interposed in the exhaust passage
on a downstream side of the first casing and contains an exhaust
purification device; a connecting pipe that connects the first and
second casings to each other and includes an insertion portion that
is inserted in the first casing, the connecting pipe being provided
in the insertion portion with a plurality of through-holes
connecting the inside and outside of the connecting pipe, thus
introducing exhaust gas within the first casing into the connecting
pipe through the through-holes, and guiding the exhaust gas towards
the second casing; and an injection nozzle that has a tip end
inserted in the connecting pipe and injects an auxiliary agent
required for the exhaust purification device from the tip end.
2. The exhaust purification apparatus for an engine according to
claim 1, wherein: the first casing has a substantially cylindrical
shape; the second casing is placed on a lateral side with regard to
a central axis of the first casing; and the connecting pipe is
disposed so that an upstream-side portion thereof extends from one
portion of a lateral face of the first casing through to another
portion of the lateral face, and the through-holes are formed in
the insertion portion that is located inside the first casing.
3. The exhaust purification apparatus for an engine according to
claim 2, wherein: the connecting pipe is provided with the
through-holes so that diameters of the through-holes located
downstream as seen in an exhaust flow direction in the first casing
are larger than those of the through-holes located upstream.
4. The exhaust purification apparatus for an engine according to
claim 2, wherein: the through-holes having virtually the same
diameter are substantially uniformly arranged in the insertion
portion of the connecting pipe.
5. The exhaust purification apparatus for an engine according to
claim 1, wherein: the connecting pipe is provided with the
through-holes so that total opening area of the through-holes is
larger than passage-sectional area of the connecting pipe.
6. The exhaust purification apparatus for an engine according to
claim 1, wherein: the injection nozzle injects the auxiliary agent
from the upstream side as considered in the exhaust flow direction
towards the downstream side along a central axis of the connecting
pipe.
7. The exhaust purification apparatus for an engine according to
claim 1, wherein: the first casing has a substantially cylindrical
shape; the second casing is placed in a direction of a central axis
of the first casing; one end of the connecting pipe is connected to
the second casing and extends from the second casing towards the
first casing, so that a portion located on a side of the other end
of the connecting pipe is inserted into the first casing through an
end portion of the first casing, which is located on a side of the
second casing; and the injection nozzle injects the auxiliary agent
from a side of the end of the connecting pipe, which is located
within the first casing.
8. The exhaust purification apparatus for an engine according to
claim 1, wherein: the injection nozzle injects a urea aqueous
solution as the auxiliary agent; and the exhaust purification
device is a selective reduction type NOx catalyst for reducing NOx
contained in exhaust gas by using ammonia produced from the urea
aqueous solution that is injected from the injection nozzle.
9. The exhaust purification apparatus for an engine according to
claim 1, wherein: the injection nozzle injects fuel as the
auxiliary agent; and the exhaust purification device is a pre-stage
oxidation catalyst for forcibly regenerating a diesel particulate
filter that is set downstream thereof, by causing an oxidation
reaction of the fuel injected from the injection nozzle and
increasing exhaust temperature.
10. The exhaust purification apparatus for an engine according to
claim 1, wherein: the injection nozzle injects fuel as the
auxiliary agent; and the exhaust purification device is a pre-stage
oxidation catalyst for carrying out a SOx purge of an absorption
type NOx catalyst that is set downstream thereof by causing an
oxidation reaction of the fuel injected from the injection nozzle
and increasing the exhaust temperature.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust purification
apparatus for an engine, and more specifically, to an exhaust
purification apparatus in which an auxiliary agent is injected from
an injection nozzle into exhaust gas flowing through an exhaust
passage, and is supplied to an exhaust purification device.
BACKGROUND ART
[0002] For example, an exhaust purification apparatus with an SCR
catalyst (selective reduction type NOx catalyst) has been known as
one in which an auxiliary agent is injected into exhaust gas and
supplied to an exhaust purification device. As is well known, the
SCR catalyst needs NH.sub.3 (ammonia) for reducing NOx contained in
exhaust gas. In the exhaust purification system, a urea aqueous
solution is injected as a reducing agent acting as an auxiliary
agent from an injection nozzle disposed upstream of the SCR
catalyst interposed in the exhaust passage. The NH.sub.3 produced
by the urea aqueous solution being hydrolyzed by exhaust heat and
water vapor contained in exhaust gas is used to accomplish a NOx
reducing action of the SCR catalyst.
[0003] The NOx reducing action in the SCR catalyst is greatly
influenced by the supply condition of the urea aqueous solution. In
other words, in order to accomplish a good reducing action, it is
necessary to supply NH.sub.3 to each section of the SCR catalyst as
evenly as possible by fully dispersing and atomizing the urea
aqueous solution in the exhaust gas, and preventing the urea
aqueous solution from adhering to the wall surfaces of the exhaust
passage and the like. To fulfill such a need, various measures have
been suggested, which place an exhaust-gas agitating device in an
exhaust passage. Such measures are disclosed, for example, in
Unexamined Japanese Patent Publication No. 2006-29233 (hereinafter,
referred to as Patent Document 1).
[0004] In an exhaust purification apparatus disclosed in Patent
Document 1, as shown in FIGS. 1 and 2, a fin device with four fins,
which functions as agitating means, is set upstream of an injection
nozzle of an exhaust passage. When exhaust gas passes through the
fin device, there generates a swirl flow by the action of the fins.
This accelerates a urea aqueous solution to disperse into the
exhaust gas.
[0005] In order to create a strong swirl flow that is proper to
accelerate the dispersion of the urea aqueous solution by using the
fin device, it is required to secure a decently wide fin area and
set a fin angle large so that the exhaust flow direction may be
changed at a steep angle. However, passage area at a position of
the fin device is narrowed along with an increase of the fin area.
At the same time, the increase of the fin angle changes the exhaust
flow direction at a steep angle, leading to an increase in pressure
loss. This results in an increase in exhaust pressure of the
engine, which causes a deterioration in operative performance. In
addition, a portion of the injected urea aqueous solution easily
adheres to the inner circumferential surface of the exhaust passage
due to the centrifugal force of the swirl flow. Such a phenomenon,
too, becomes a factor in hindrance to the dispersion and
atomization of the urea aqueous solution.
[0006] In this respect, there is still room for improvement in the
exhaust purification apparatus disclosed in Patent Document 1
because there is a trade-off relationship between the acceleration
of dispersion and atomization of the urea aqueous solution and the
inhibition of an increase in engine exhaust pressure, and it is
impossible to achieve both of these two at a high level.
DISCLOSURE OF THE INVENTION
[0007] The invention has been made in light of the above problems.
An object of the present invention is to provide an exhaust
purification apparatus for an engine, which is capable of achieving
both the acceleration of dispersion and atomization of an auxiliary
agent and the inhibition of an increase in engine exhaust pressure
at a high level, and thereby delivering good purification
performance.
[0008] In order to accomplish the object, the exhaust purification
apparatus for an engine according to the present invention
comprises a first casing that is interposed in an exhaust passage
of the engine; a second casing that is interposed in the exhaust
passage on a downstream side of the first casing and contains an
exhaust purification device; a connecting pipe that connects the
first and second casings to each other and includes an insertion
portion that is inserted in the first casing, the connecting pipe
being provided in the insertion portion with a plurality of
through-holes connecting the inside and outside of the connecting
pipe, thus introducing exhaust gas within the first casing into the
connecting pipe through the through-holes, and guiding the exhaust
gas towards the second casing; and an injection nozzle that has a
tip end inserted in the connecting pipe and injects an auxiliary
agent required for the exhaust purification device from the tip
end.
[0009] In the exhaust purification apparatus for an engine
according to the present invention, the exhaust gas of the engine
is introduced through the exhaust passage into the first casing.
Subsequently, in the first casing, the exhaust gas is introduced
into the connecting pipe through the through-holes of the
connecting pipe. The exhaust gas introduced into the connecting
pipe is then guided through the connecting pipe into the second
casing to flow into the exhaust purification device. Streams of the
exhaust gas introduced into the connecting pipe through the
through-holes of the connecting pipe collide with each other within
the connecting pipe to be agitated. The auxiliary agent is injected
from the injection nozzle towards the exhaust gas that is in the
process of this agitation. The auxiliary agent is therefore
transmitted to the second-casing side in a fully dispersed and
atomized state. Moreover, the exhaust gas that is jetted out
through the through-holes into the connecting pipe prevents the
auxiliary agent from adhering to an inner circumferential surface
of the connecting pipe, which also contributes to the acceleration
of dispersion and atomization of the auxiliary agent. This
suppresses a biased distribution of the auxiliary agent that is
supplied to each section of the exhaust purification device located
downstream, and therefore, due to the supplied adjuvant, an exhaust
purifying effect of the exhaust purification device is properly
exhibited.
[0010] Since the agitating action is carried out by making the
exhaust gas streams collide with each other within the connecting
pipe, even if total opening area of the through-holes is slightly
increased to inhibit an increase in pressure loss that is generated
when the exhaust gas flows, the agitating action is not
discouraged. This makes it possible to achieve both the
acceleration of dispersion and atomization of the auxiliary agent
and the inhibition of an increase in engine exhaust pressure at a
high level.
[0011] The exhaust purification apparatus for an engine according
to the present invention is capable of delivering good purification
performance by suppressing the biased distribution of the auxiliary
agent supplied to each section of the exhaust purification device,
and is also capable of achieving good operative performance by
inhibiting an increase in engine exhaust pressure.
[0012] In the exhaust purification apparatus for an engine
according to the invention, for example, the first casing may have
a substantially cylindrical shape, and the second casing may be
placed on a lateral side with regard to a central axis of the first
casing. In this case, the connecting pipe is disposed so that an
upstream-side portion thereof extends from one portion of a lateral
face of the first casing through to another portion of the lateral
face, and the through-holes are formed in the insertion portion
that is located inside the first casing. Furthermore, in this case,
the connecting pipe may be provided with the through-holes so that
diameters of the through-holes located downstream as seen in an
exhaust flow direction in the first casing are larger than those of
the through-holes located upstream. If the diameters of the
through-holes are differentiated in this way, the auxiliary agent
is better dispersed and atomized according to a change in a flow
condition of the exhaust gas flowing from the first casing to the
connecting pipe. However, even if the through-holes having
virtually the same diameter are substantially uniformly arranged in
the insertion portion of the connecting pipe, the auxiliary agent
can be well dispersed and atomized.
[0013] In the exhaust purification apparatus for an engine
according to the present invention, for example, the connecting
pipe may be provided with the through-holes so that total opening
area of the through-holes is larger than passage-sectional area of
the connecting pipe. This effectively inhibits an increase in
engine exhaust pressure, which is caused by making the exhaust gas
run through the through-holes.
[0014] In the exhaust purification apparatus for an engine
according to the present invention, for example, the injection
nozzle may inject the auxiliary agent from the upstream side as
considered in the exhaust flow direction towards the downstream
side along a central axis of the connecting pipe. This makes it
possible to effectively accelerate the dispersion and atomization
of the auxiliary agent and further reliably prevent the auxiliary
agent from adhering to the inner circumferential surface of the
connecting pipe.
[0015] In the exhaust purification apparatus for an engine
according to the present invention, for example, the first casing
may have a substantially cylindrical shape, and the second casing
may be placed in a direction of the central axis of the first
casing. In this case, one end of the connecting pipe is connected
to the second casing and extends from the second casing towards the
first casing, so that a portion located on a side of the other end
of the connecting pipe is inserted into the first casing through an
end portion of the first casing, which is located on a side of the
second casing. The injection nozzle injects the auxiliary agent
from a side of the end of the connecting pipe, which is located
within the first casing.
[0016] In the exhaust purification apparatus for an engine
according to the present invention, for example, the injection
nozzle may inject a urea aqueous solution as the auxiliary agent.
In this case, the exhaust purification device is a selective
reduction type NOx catalyst for reducing NOx contained in exhaust
gas by using ammonia produced from the urea aqueous solution that
is injected from the injection nozzle. This suppresses a biased
distribution of ammonia that is supplied to the selective reduction
type NOx catalyst, so that the selective reduction type NOx
catalyst exhibits a good exhaust purification function.
[0017] In the exhaust purification apparatus for an engine
according to the present invention, for example, the injection
nozzle may inject fuel as the auxiliary agent. In this case, the
exhaust purification device is a pre-stage oxidation catalyst for
forcibly regenerating a diesel particulate filter that is set
downstream thereof, by causing an oxidation reaction of the fuel
injected from the injection nozzle and increasing exhaust
temperature. Alternatively, in this case, the exhaust purification
device is a pre-stage oxidation catalyst for carrying out a SOx
purge of an absorption type NOx catalyst that is set downstream
thereof by causing an oxidation reaction of the fuel injected from
the injection nozzle and increasing the exhaust temperature. This
suppresses a biased distribution of fuel that is supplied to the
pre-stage oxidation catalyst, so that the exhaust temperature can
be efficiently increased by the oxidation reaction of the fuel in
the pre-stage oxidation catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a view showing an entire configuration of an
exhaust purification apparatus for an engine according to an
embodiment of the present invention;
[0019] FIG. 2 is a partial enlarged sectional view showing a
connection between first and second casings as a first embodiment
of the present invention;
[0020] FIG. 3 is a partial enlarged sectional view showing an
exhaust flow state correspondingly to FIG. 2;
[0021] FIG. 4 is a partial enlarged sectional view showing a
connection between the first and second casings as a second
embodiment of the present invention;
[0022] FIG. 5 is a sectional view showing an exhaust flow state,
taken along line V-V of FIG. 4; and
[0023] FIG. 6 is a partial enlarged sectional view showing a
connection between the first and second casings as a third
embodiment of the present invention.
BEST MODE OF CARRYING OUT THE INVENTION
[0024] An exhaust purification apparatus for an engine according to
a first embodiment of the present invention will be described below
in details with referenced to the drawings.
[0025] FIG. 1 is a view showing an entire configuration of the
exhaust purification apparatus for an engine according to the first
embodiment. An engine 1 is an in-line six-cylinder diesel engine.
The engine 1 and an exhaust purification apparatus 2 of the first
embodiment are installed in a truck. FIG. 1 schematically shows the
engine 1 and the exhausts purification apparatus 2 in the same
layout as in an actual placement in the truck, and partially shows
an underfloor area of the truck. In the following descriptions, a
longitudinal direction and a horizontal direction are defined on
the basis of a vehicle.
[0026] The truck employs a chassis structure with a ladder frame.
The ladder frame is constructed by connecting a pair of right and
left side rails 3a to each other, which extend in an entire
longitudinal direction of a vehicle body, by means of a plurality
of cross members 3b (FIG. 1 shows only one). In addition to power
plants including the engine 1 and so on, a cabin, a cargo bed 3c,
etc., which form the vehicle body, are mounted on the ladder frame.
FIG. 1 partially shows the pair of right and left side rails 3a of
the ladder frame, and also shows the cargo bed 3c mounted on the
ladder frame by chain double-dashed lines. The exhaust purification
apparatus 2 is placed in the underfloor area located beneath the
cargo bed 3c.
[0027] The engine 1 is disposed between the right and left side
rails 3a forming the ladder frame. A fuel injection valve 4 is
provided to each cylinder of the engine 1. The fuel injection
valves 4 are supplied with pressurized fuel from a common rail 5,
and inject fuel into the corresponding cylinders when the valves
are opened. Mounted on an intake side of the engine 1 is an intake
manifold 6 for supplying intake air to the engine 1. In an intake
passage 7 connected to the intake manifold 6, there are interposed
an air cleaner 8, a compressor 9a of a turbocharger 9, and an
intercooler 10, in the order from upstream to downstream. An
exhaust manifold 12 for discharging the exhaust gas of the engine 1
is mounted on an exhaust side of the engine 1. A turbine 9b of the
turbocharger 9, which is mechanically and coaxially connected to
the compressor 9a, is fixed to an outlet of the exhaust manifold
12. An exhaust passage 13 is connected to the turbine 9b. The
exhaust purification apparatus 2 is interposed in the exhaust
passage 13.
[0028] A transmission 15 is attached to a rear portion of the
engine 1. An output shaft of the transmission 15 is connected to a
front end of a propeller shaft 16. The propeller shaft 16 extends
rearwards between the right and left side rails 3a in the
underfloor area of the vehicle body. A rear end of the propeller
shaft 16 is connected to right and left rear wheels through
differential gears, not shown.
[0029] The exhaust passage 13 extends rearwards between the
propeller shaft 16 and the right side rail 3a in the underfloor
area of the vehicle body. In the case of a conventional truck, the
exhaust passage 13 extends directly to the rear portion of the
vehicle body, and component members of the exhaust purification
apparatus 2 are serially arranged in the exhaust passage 13. In the
truck of the present embodiment, however, there is not enough
longitudinal space because of the length of the cargo bed. For this
reason, the exhaust passage 13 is deflected to the right so that
exhaust gas is discharged in a lateral direction. According to such
deflection of the exhaust passage 13, the layout of the exhaust
purification apparatus 2 interposed in the exhaust passage 13 is
also anomalous. A configuration of the exhaust purification
apparatus 2 will be described below in details.
[0030] A first casing 17 is connected to the exhaust passage 13
between the propeller shaft 16 and the right side rail 3a. The
first casing 17 has a cylindrical shape with a central axis
extending along the longitudinal direction (exhaust flow
direction). A pre-stage oxidation catalyst 18 is arranged on the
upstream side in the first casing 17, and a wall-flow type DPF
(diesel particulate filter) 19 for collecting PM (particulate
matter) contained in exhaust gas is arranged on the downstream side
in the first casing 17. In the first casing 17, furthermore, a
space called a mixing chamber 20 is formed downstream of the DPF
19. A fuel injection valve 21 for forcible regeneration of the DPF
19, which will be described later, is interposed in the exhaust
passage 13 in a position close to the first casing 17.
[0031] FIG. 2 is a partial enlarged sectional view showing a
connection between the first and second casings in the exhaust
purification apparatus 2. As shown in FIGS. 1 and 2, a connecting
pipe 22 is laid in a position corresponding to the mixing chamber
20 of the first casing 17, running through the first casing 17 in
the lateral direction (namely, a direction intersecting the central
axis of the first casing 17). The connecting pipe 22 makes up a
part of the exhaust passage 13 and has a diameter that is
substantially equal to that of the exhaust passage 13. The first
casing 17 and the connecting pipe 22 are welded together at
piercing portions of the connecting pipe 22. A lid 22b is welded to
a left end of the connecting pipe 22, which is exposed from an
outer circumferential surface of the first casing 17, thereby
closing the left end of the connecting pipe 22.
[0032] In a portion (inserted portion) of the connecting pipe 22,
which is exposed within the mixing chamber 20, there are formed a
large number of through-holes 22a for connecting the inside and
outside of the connecting pipe 22. The inside of the mixing chamber
20 and that of the connecting pipe 22 communicate with each other
through the through-holes 22a. The through-holes 22a of the
connecting pipe 22 have identical diameters and are so arranged as
to disperse uniformly in the exposed portion in the mixing chamber
20. Total opening area of all the through-holes 22a is set larger
than passage-sectional area of the connecting pipe 22. However, the
total opening area is not necessarily determined as describe, and
may be smaller than the passage-sectional area of the connecting
pipe 22.
[0033] A second casing 23, which has a cylindrical shape with a
central axis extending in the lateral direction, is placed on the
right side of the first casing 17 across the right side rail 3a.
The connecting pipe 22 projects to the right from the outer
circumferential surface of the first casing 17, and extends so as
to pass under the side rail 3a and then curve in a forward
direction. A right end of the connecting pipe 22 is welded to an
outer circumferential surface of the second casing 23 in a position
located on a left-end side of the second casing 23. On the upstream
side in the second casing 23 (namely, the left side of the
vehicle), there is disposed an SCR catalyst (selective reduction
type NOx catalyst) 24 that reduces NOx within exhaust gas by using
NH.sub.3 (ammonia). The SCR catalyst 24 corresponds to the exhaust
purification device of the invention. A post-stage oxidation
catalyst 25 is placed on the downstream side in the second casing
23 (namely, the right side of the vehicle). One end of an exhaust
pipe 26 is welded to the second casing 23 on the downstream side of
the post-stage oxidation catalyst 25. The other end of the exhaust
pipe 26 curves to the left and opens in the lateral direction of
the vehicle body. The exhaust pipe 26 makes up a part of the
exhaust passage 13.
[0034] An electromagnetic type injection nozzle 27 is attached to
the lid 22b of the connecting pipe 22 so as to be located on a
central axis L of the connecting pipe 22. The injection nozzle 27
has a tip end 27a that is inserted through the lid 22b into the
connecting pipe 22. The injection nozzle 27 is capable of injecting
a urea aqueous solution, which is pressure-fed from a tank, not
shown, into the connecting pipe 22 as a reducing agent (auxiliary
agent). A direction in which the injection nozzle 27 injects the
urea aqueous solution is set along the central axis L of the
connecting pipe 22 toward the side of the second casing 23 (namely,
downstream side).
[0035] Controllable devices including the fuel injection valves 2
of the cylinders of the engine 1, the fuel injection valve 21 for
forcible regeneration, the injection nozzle 27, etc., and sensors,
not shown, are electrically connected to an ECU (electrical control
unit) 31. The controllable devices are driven and controlled by the
ECU 31 according to the detected information that is transmitted
from the sensors. For example, the ECU 31 operates the engine 1 by
controlling an injection amount, injection pressure, and injection
timing of the fuel injection valves 2 according to an operating
condition of the engine 1, which includes revolution speed, load,
and the like.
[0036] During the operation of the engine 1, the exhaust gas
discharged from the engine 1 flows through the exhaust passage 13
and is introduced into the first casing 17. After passing through
the pre-stage oxidation catalyst 18 and the DPF 19, the exhaust gas
flows into the mixing chamber 20. The exhaust gas that has flown
into the mixing chamber 20 is introduced into the connecting pipe
22 through the through-holes 22a of the connecting pipe 22. The
exhaust gas then flows through the connecting pipe 22 and flows
into the second casing 23. Subsequently, the exhaust gas passes
through the SCR catalyst 24 and the post-stage oxidation catalyst
25, and is discharged into the atmosphere through the exhaust pipe
26. During this process, the PM contained in the exhaust gas is
collected in the DPF 19, and the NOx contained in the exhaust gas
is reduced in the SCR catalyst 24. Due to these actions of the DPF
19 and the SCR catalyst 24, the exhaust gas is purified, and
harmful components are prevented from being discharged into the
atmosphere. In order to make the DPF 19 and the SCR catalyst 24
properly exhibit such purifying operations, the ECU 31 implements a
forcible regeneration control with respect to the DPF 19, and
implements a control on the supply of the urea aqueous solution,
which is carried out by the injection nozzle 27, with respect to
the SCR catalyst 24. Hereinafter, these controls will be described
below in details.
[0037] As the PM is collected, a deposit amount of the PM in the
DPF 19 gradually increases. The PM collected in the DPF 19 is
continuously burnt and removed (continuous regeneration) by using
NO.sub.2, which is created by an oxidation reaction of NO contained
in the exhaust gas in the pre-stage oxidation catalyst 18, as an
oxidant, when the engine 1 is operated in a prescribed operating
condition (for example, an operating condition in which exhaust
temperature is relatively high). If an operating condition of the
engine 1, in which the continuous regeneration of the DPF 19 is not
achieved, continues for long, the deposit amount of the PM in the
DPF 19 increases by degree and exceeds a tolerable amount. In
preparation for such a situation, the ECU 31 performs the forcible
regeneration for forcibly burning and removing the PM deposited in
the DPF 19, before the PM deposit amount that is estimated from the
operating condition of the engine 1 exceeds the tolerable amount.
The fuel injection valve 21 located in the exhaust passage 13 is
used in the forcible regeneration. The ECU 31 makes the fuel
injection valve 21 inject unburned fuel and thus supplies the
unburned fuel to the pre-stage oxidation catalyst 18. Oxidation
reaction heat of the unburned fuel increases the temperature of the
DPF 19 located downstream, thereby burning and removing the PM
deposited in the DPF 19. Instead of supplying the unburned fuel
from the fuel injection valve 21, the unburned fuel may be supplied
from the fuel injection valves 2 to the pre-stage oxidation
catalyst 18 by post injection during an expansion stroke or exhaust
stroke after main injection.
[0038] In the supply control of the urea aqueous solution, ECU 31
controls an injection amount of the urea aqueous solution injected
from the injection nozzle 27 according to the operating condition
of the engine 1, a detected value of a temperature sensor, not
shown, which is disposed near the injection nozzle 27, etc. The
urea aqueous solution that has been injected is hydrolyzed by
exhaust heat and water vapor contained in exhaust gas in the
process of flowing through the connecting pipe 22, to thereby
produce NH.sub.3. The NH.sub.3 thus produced is transmitted to the
SCR catalyst 24 located downstream, and is used in the SCR catalyst
24 to reduce NOx contained in the exhaust gas to harmless N.sub.2.
The NH.sub.3 left in the SCR catalyst 24 is processed by the
post-stage oxidation catalyst 25. The post-stage oxidation catalyst
25 further processes CO produced by burning the PM in the DPF
19.
[0039] The NOx reducing action in the SCR catalyst 24 is greatly
influenced by the supply condition of the urea aqueous solution
from the injection nozzle 27. In the present embodiment, therefore,
the urea aqueous solution is injected into the connecting pipe 22
provided with a large number of through-holes 22a as described
above. Operation and advantages which are obtained by the foregoing
configuration will be described below.
[0040] FIG. 3 is a partial enlarged sectional view showing an
exhaust flow state correspondingly to FIG. 2. In the mixing chamber
20 of the first casing 17, the exhaust gas is introduced into the
connecting pipe 22 through the through-holes 22a. In the connecting
pipe 22, as shown by arrows, streams of the exhaust gas are
collected from the entire circumference of the connecting pipe 22
to the center thereof through the through-holes 22a formed in the
circumference of the connecting pipe 22. The exhaust gas streams
then flow towards the second casing 23 located downstream while
colliding with each other. As a result of the mutual collision, the
exhaust gas is vigorously agitated. The urea aqueous solution is
injected from the injection nozzle 27 into the exhaust gas in the
process of being agitated. As a result, the urea aqueous solution
that has been injected is transmitted toward the second casing 23
in a state fully dispersed and atomized within the exhaust gas.
[0041] The exhaust gas that is jetted out through the through-holes
22a formed in the entire circumference of the connecting pipe 22
accelerates the dispersion and atomization of the urea aqueous
solution within the connecting pipe 22, and prevents the urea
aqueous solution from adhering to an inner circumferential surface
of the connecting pipe 22. The urea aqueous solution that has once
adhered to the inner circumferential surface is hard to disperse
and atomize in the exhaust gas, so that the adhesion-preventing
effect also contributes to the acceleration of the dispersion and
atomization.
[0042] In addition, the agitating action in the connecting pipe 22
is the most active in the central area where the exhaust gas
streams collide with each other. The urea aqueous solution is
injected from the injection nozzle 27 along the central axis L of
the connecting pipe 22. The urea aqueous solution being transmitted
through the connecting pipe 22 is therefore continuously exposed to
the vigorous agitating action. Consequently, the urea aqueous
solution is further reliably dispersed and atomized, and is
prevented from adhering to the inner circumferential surface of the
connecting pipe 22 without fail.
[0043] Due to the foregoing factors, the urea aqueous solution
injected into the connecting pipe 22 is fully dispersed and
atomized in exhaust gas, and the NH.sub.3 produced by hydrolysis of
the urea aqueous solution within the connecting pipe 22 is
substantially uniformly supplied to each section of the SCR
catalyst 24 located downstream. The NOx reducing action of the SCR
catalyst 24 is thus optimized, and reliably reduces the NOx
contained in exhaust gas, to thereby purify the exhaust gas.
[0044] Since the total opening area of the through-holes 22a of the
connecting pipe 22 is larger than the passage-sectional area of the
connecting pipe 22, there is no such trouble that pressure loss is
increased by causing the exhaust gas to flow through the
through-holes 22a. It is therefore possible to prevent an increase
in exhaust pressure of the engine 1.
[0045] In other words, according to the exhaust purification
apparatus 2 of the present embodiment, even if the total opening
area of the through-holes 22a is slightly increased to prevent an
increase in pressure loss, this does not discourage the agitating
action on the exhaust gas, which is caused by the through-holes
22a. Consequently, in the exhaust purification apparatus 2 of the
present embodiment, the acceleration of dispersion and atomization
of the urea aqueous solution and the inhibition of an increase in
exhaust pressure of the engine 1 are not always in a trade-off
relationship. The exhaust purification apparatus 2 of the present
embodiment then achieves both the acceleration of dispersion and
atomization of the urea aqueous solution and the inhibition of an
increase in exhaust pressure of the engine 1 at a high level, and
also accomplishes both a good exhaust-purifying performance and a
good operating performance.
[0046] In the exhaust purification apparatus 2 of the present
embodiment, the injection nozzle 27 is set at the left end (namely,
the upstream side) of the connecting pipe 22 disposed so as to
extend through the first casing 17. As shown in FIG. 3, distance A
between the injection nozzle 27 and the SCR catalyst 24 is long,
which makes it possible to secure a maximum amount of time required
for the urea aqueous solution to reach the SCR catalyst 24 through
the connecting pipe 22. This factor, too, contributes to the
acceleration of dispersion and atomization of the urea aqueous
solution.
[0047] The mixing chamber 20 is required to have a certain amount
of capacity as the connecting pipe 22 needs to penetrate through
the mixing chamber 20, and the mixing chamber 20 is located on the
most downstream side in the first casing 17 containing the
pre-stage oxidation catalyst 18 and the DPF 19. For this reason,
the exhaust purification apparatus 2 of the present embodiment has
the advantage of being reduced in size, as compared to an
apparatus, for example, in which the mixing chamber 20 is
interposed in the exhaust passage 13 of the engine 1 separately
from the first casing 17.
[0048] An exhaust purification apparatus 2' for the engine 1
according to a second embodiment of the present invention will be
described below in details with referenced to the drawings.
Comparing the exhaust purification apparatus 2' of the present
embodiment with the exhaust purification apparatus 2 of the first
embodiment, a connecting pipe 41 has a different configuration from
that of the connecting pipe 22 shown in FIG. 2. The entire
configuration of the exhaust purification apparatus 2' is identical
to that of the exhaust purification apparatus 2 of the first
embodiment as illustrated in FIG. 1. The components identical to
those of the first embodiment will be provided with the same
reference marks, and descriptions thereof will be omitted. In the
following descriptions, a focus will be on differences with the
first embodiment.
[0049] FIG. 4 is a partial enlarged sectional view showing a
connection between the first casing 17 and the second casing 23.
FIG. 5 is a sectional view showing an exhaust flow state, taken
along line V-V of FIG. 4. A plurality of through-holes 41a and 41b
are formed in a part (inserted part) of the connecting pipe 22,
which is exposed in the mixing chamber 20 of the first casing 17.
The through-holes 41a and 41b are arranged so as to uniformly
disperse like the through-holes 22a of the first embodiment. In
common with the first embodiment, total opening area of the
through-holes 41a and 41b is set larger than passage-sectional area
of a connecting pipe 41. According to the present embodiment, the
through-holes 41a and 41b formed in the connecting pipe 41 are
roughly divided into large-diameter holes and small-diameter holes.
Concretely speaking, if a virtual plane vertically expanding along
a central axis L of the connecting pipe 41 is seen as a boundary,
the small-diameter through-holes 41a are disposed on the upstream
side of the exhaust flow direction (namely, DPF 19-side), and the
large-diameter through-holes 41b are disposed on the downstream
side of the exhaust flow direction (namely, opposite side to the
DPF 19).
[0050] The through-holes 41a and 41b have diameters that are
determined in consideration of the following points. As shown in
FIG. 5, flow conditions of the exhaust gas that has passed through
the DPF 19 and flows toward the through-holes 41a and 41b differ
depending upon the portions of the connecting pipe 41. As shown by
arrows in FIG. 5, the exhaust gas that has passed through the DPF
19 flows directly into the through-holes 41a located on the
upstream side of the exhaust flow direction, while the exhaust gas
that has passed through the DPF 19 flows into the through-holes 41b
located on the downstream side of the exhaust flow direction after
the exhaust gas collides with an inner wall of the first casing 17
and returns. Because of this difference, it is hard for the exhaust
gas to flow into the through-holes 41b located on the downstream
side of the exhaust flow direction, as compared to the
through-holes 41a located on the upstream side. Such a gap between
the flow conditions incurs uneven agitation of the exhaust gas
within the connecting pipe 41, which might eventually hampers the
dispersion and atomization of the urea aqueous solution serving as
a reducing agent (auxiliary agent).
[0051] In the exhaust purification apparatus 2' of the present
embodiment, the through-holes 41b located on the downstream side of
the exhaust flow direction have a larger diameter than the
through-holes 41a located on the upstream side as described above,
thereby reducing the gap between the flow conditions of the exhaust
gas flowing into the through-holes 41a and 41b. The exhaust gas is
thus well agitated within the connecting pipe 41. Consequently,
when the exhaust gas is introduced into the connecting pipe 41
through the through-holes 41a and 41b, the agitating action is
optimized. For this reason, it is possible to accomplish the better
dispersion and atomization of the urea aqueous solution, preventing
an increase in exhaust pressure of the engine 1, as compared to the
exhaust purification apparatus 2 of the first embodiment. As a
result, it is possible to further improve the exhaust purifying
effect accomplished by the SCR catalyst 24 that reduces the
NOx.
[0052] The present embodiment determines the two different
diameters as to the through-holes 41a and 41b of the connecting
pipe 41. However, the diameters are not limited to these two kinds.
For example, the diameters of the through-holes 41a and 41b may be
gradually increased from the upstream side toward the downstream
side.
[0053] An exhaust purification apparatus 2'' for the engine 1
according to a third embodiment of the present invention will be
described below in details with referenced to the drawings. The
exhaust purification apparatus 2'' of the present embodiment is
different from the exhaust purification apparatus 2 of the first
embodiment in terms of the placement of the first casing 17 and the
second casing 23. Accordingly, a connecting pipe 51 is connected to
the mixing chamber 20 of the first casing 17 in a different way.
The components identical to those of the first embodiment will be
provided with the same reference marks, and descriptions thereof
will be omitted. In the following descriptions, a focus will be on
differences with the first embodiment.
[0054] FIG. 6 is a partial enlarged sectional view showing a
connection between the first casing 17 and the second casing 23. In
short, the present embodiment differs from the first and second
embodiments in which the exhaust purification apparatus 2'' is
anomalously disposed. In the present embodiment, component members
of the exhaust purification apparatus 2'' are serially arranged as
in conventional trucks. In other words, the second casing 23 is
disposed to serially continue rearwards to the first casing 17 that
contains the pre-stage oxidation catalyst 18 and the DPF 19. The
SCR catalyst 24 and the post-stage oxidation catalyst 25 are
contained in the second casing 23.
[0055] The mixing chamber 20 is formed downstream of the DPF 19 in
the first casing 17. The connecting pipe 51 extends further
forwards from the connection with the first casing 17 and is
inserted into the mixing chamber 20. A lid 51b is welded to a front
end of the connecting pipe 51 within the mixing chamber 20, and the
front end of the connecting pipe 51 is thus closed. In a portion
(inserted portion) of the connecting pipe 51, which is exposed
within the mixing chamber 20, there are formed a large number of
through-holes 51a for connecting the inside and outside of the
connecting pipe 51. In the present embodiment, as in the first
embodiment, the through-holes 51a have identical diameters and are
disposed to uniformly disperse. The shape and placement of the
through-holes 51a are not limited to this. For example, like the
second embodiment, the diameters of the through-holes 51a may be
differentiated between upstream and downstream, and/or the
through-holes 51a may be unevenly distributed.
[0056] An injection nozzle 52 is attached to one side of the outer
circumferential surface of the first casing 17. The injection
nozzle 52 has a tip end 52a, which extends through the wall of the
first casing 17 to the center of the mixing chamber 20, and is bent
in the downstream direction. The tip end 52a then passes through
the center of the lid 51b and is inserted into the connecting pipe
51.
[0057] In the exhaust purification apparatus 2'' of the present
embodiment, which is constructed in the above-described manner, the
ECU 31 controls the supply condition of the urea aqueous solution
serving as a reducing agent (auxiliary agent) from the injection
nozzle 27 as in the first embodiment. Exhaust gas is introduced
into the connecting pipe 51 through the through-holes 51a in the
mixing chamber 20. In the connecting pipe 51, the exhaust gas is
agitated in the same manner as in the first embodiment. The urea
aqueous solution is injected from the injection nozzle 27 into the
exhaust gas being agitated, and thus, the dispersion and
atomization of the urea aqueous solution is accelerated.
Consequently, the operation and advantages mentioned under the
first embodiment are also obtained in the present embodiment. Here,
repetitive descriptions is omitted.
[0058] This is the end of the description of the embodiments of the
present invention. However, an aspect of the present invention is
not limited to the above embodiments. For example, in the
above-described embodiments, the invention is applied to the
exhaust purification apparatus of the diesel engine equipped with
the SCR catalyst 24. The invention, however, is not applied
exclusively to this system. For example, in some cases, a gasoline
engine has the SCR catalyst 24 in consideration of lean-burn
operation. The invention may be applied to such a gasoline
engine.
[0059] In the above-described embodiments, the exhaust gas is
agitated within the connecting pipe 22, 41 or 51 for the dispersion
and atomization of the urea aqueous solution that is supplied to
the SCR catalyst 24. However, the application of the agitated
exhaust gas is not limited to this. For example, as is clear from
the descriptions of the DPF 19 used in the embodiments, during the
forcible regeneration that raises the temperature of the DPF 19 by
causing an oxidation reaction of unburned fuel (auxiliary agent)
supplied from the fuel injection valve 21 in the pre-stage
oxidation catalyst 18, the unburned fuel is preferably supplied to
each section of the pre-stage oxidation catalyst 18 as evenly as
possible in order to optimize the oxidation reaction of the
unburned fuel, which is caused by the pre-stage oxidation catalyst
18. To that end, a mixing chamber 20 with a connecting pipe similar
to the ones used in the embodiments may be provided on the upstream
side of the pre-stage oxidation catalyst 18, and the dispersion and
atomization of the unburned fuel may be carried out by injecting
the unburned fuel from the fuel injection valve 21 provided to the
connecting pipe into the exhaust gas that is agitated in the
connecting pipe. In this case, the pre-stage oxidation catalyst 18
corresponds to the exhaust purification device of the
invention.
[0060] In an absorption type NOx catalyst that has been publicly
known as another NOx catalyst, there occurs a phenomenon in which
SOx (sulfur oxide), instead of NOx, is absorbed, and the catalyst
is deteriorated in purifying performance, which is called sulfur
poisoning. It is therefore necessary to set a pre-stage oxidation
catalyst on the upstream side of the NOx catalyst and implement SOx
purge for removing the absorbed SOx by increasing the temperature
of the NOx catalyst with the oxidation reaction heat of the
unburned fuel (auxiliary agent) in the pre-stage oxidation
catalyst. In order to carry out the SOx purge, a construction
similar to the one in which the invention is applied for the
forcible regeneration of the DPF 19 may be employed. In this case,
too, the pre-stage oxidation catalyst corresponds to the exhaust
purification device of the invention.
[0061] In the above-described embodiments, the through-holes 22a,
41a, 41b and 51a are formed in the entire circumferences of the
connecting pipes 22, 41 and 51. However, it is not always necessary
to form the through-holes in the entire circumferences of the
connecting pipes. For example, the through-holes may be arranged in
two opposite longitudinal rows in the circumference of each of the
connecting pipes. In this case, too, it is possible to obtain a
good agitating action that is caused by the exhaust gas streams
colliding with each other within the connecting pipes.
* * * * *